The present invention relates to improvements in apparatus for manipulating stacks of overlapping paper sheets or the like, and more particularly to improvements in apparatus for transporting stacks between successive stations in production lines, e.g., in a production line for the making of exercise books, steno pads and analogous stationery products.
Commonly owned U.S. Pat. No. 4,603,768 granted Aug. 5, 1986 to Robert Deutschle for "Apparatus for transporting paper stacks" discloses a system of conveyors wherein two intermediate conveyors are coupled to each other for movement between positions of registry with discrete stack supplying conveyors and positions of alignment with a common stack receiving conveyor. The conveyors of the patented apparatus exhibit the advantage that they can treat the stacks gently and occupy a relatively small amount of space in spite of the fact that they can transport large numbers of stacks per unit of time. Gentle treatment of stacks is very important in many types of production lines because any, even negligible, shifting of certain sheets in a stack relative to the other sheets may prevent proper treatment of such stacks at the next-following station or stations, e.g., at a station where the sheets of a stack are to be provided with holes for reception of spiral binders or the like. Attempts to prevent misaligned sheets from interfering with satisfactory processing of the stacks include the provision of discrete aligning units at the stations which follow the conveyors. This contributes to the initial and maintenance cost of the production line and to space requirements of the stations.
Certain instability of stacks which are transported in a production line of the type disclosed in U.S. Pat. No. 4,603,768 is attributable to entrapment of some air between the sheets of the stacks, mainly during accumulation of sheets into stacks. As a rule, entrapped air will escape with time but the interval which is required for the escape of entrapped air is often too long, especially in a modern production line which must turn out large numbers of pads or like products per unit of time. In addition, it is normally desirable to place successive sheet- and stack-processing stations close or very close to each other as well as to operate the stack-transporting conveyors at an elevated speed. This even further reduces the likelihood of spontaneous expulsion or escape of air before a stack reaches that station where the bodies of entrapped air might interfere with predictable processing of the stacks and/or before the entrapped air causes a shifting of one or more sheets in the respective stack.